Signaling systems



2,713,654 SIGNALKNG SYSTEMS Theodor Frankel, Rochester, N. 1., assignor to Stronn her -Carison Comuan a cor oration of New York This invention relates to signaling systems and particul."

larly to control circuits operated over su' scriber station lines for controlling switching means for interconnecting stations in a communication system.

The object of the invention is to increase the reliability of operation of switching means, particularly under adverse plant conditions. Where a telephone exchange area is compact and single party lines are employed there is little difficulty in establishing and maintaining minimum subscriber line conditions under which the central office apparatus will operate satisfactorily. However, there are situations encountered in practice particularly in rural communities Where multiparty lines are used where the line impedance may exceed the limiting values and in such cases careful maintenance practices must be adhered to, with the result that the maintenance costs to prevent unsatisfactory operation may become unduly high. ticular Where the number of parties on a line exceeds some figure such as five and the capacit I across the line reaches an appreciable figure, or where there is low resistance leakage across the line so the calling bridge relay tends 2.;

to release slowly, reliable operation is secured only at the expense of costly maintenance or additional special devices. The object of the present invention may then be restated as an effort to provide means which will respond uniformly to any condition likely to be met in practice and to eliminate the need for especially expert maintenance personnel.

The invention consists in the employment of a transient current produced on the closing of a circuit for effectively holding the said circuit firmly closed until the normal response thereto has been completed.

In a preferred embodiment of the invention the switchthrough whose windings the line current to the calling subscriber station is fed. When the switch is seized this relay is operated through the closed calling subscribers loop, and its function is to respond to the dial pulses, each of which consists of a temporary opening of this loop circuit. thereof is low, the calling bridge relay will respond firmly to the dial pulses and the periods of operation and release thereof will reflect almost exactly the pattern of the dial.

instruments or its impedance is otherwise affected so 59 current generated by and at the beginning of a pulse, con- 7 sisting of a momentary release of the calling bridge relay, is employed to maintain the effect intended to be produced If the subscribers loop is clear and the resistance t Heretofore careful adjustment of the 6:

by this relay even though this relay fails to rem released condition long enough to insure a satisfactory response.

The calling bridge relay in certain conventional circuits operates a lock-pulse (LP) or hunt-assist (HA) relay which in turn closes a stepping magnet circuit. In one embodiment of the invention where the current through the stepping magnet is comparatively heavy, its battery feed connection is made through the primary winding of a transformer and the secondary Winding of this trans former is connected to a separate winding of the lock-pulse relay. Therefore, as the said lock-pulse relay closes the circuit of the stepping magnet the rise of current therein produces a transient current in the secondary of the said transformer which in a properly poled secondary winding of the lock-pulse relay holds this relay firmly operated until this transient dies down. The stepping magnet will completely operate its armature before the current in its winding has reached its final value or, otherwise stated, before the change in value thereof has reached a Zero level.

In another embodiment of the invention a separate winding of the lock-pulse or hunt-assist relay is connected in series with a condenser and the circuit thereof is controlled by an armature and contacts of the relay so that upon the operation of the relay the condenser is placed in a charging circuit. Through proper design of the condenser and the relay winding the charging current may be employed to hold the relay firmly operated for a period sufficient to insure the proper operation of the stepping magnet.

The advantages of this design include unlimited life, no maintenance costs, universal use on all subscriber lines,

conventional switching apparatus since less critical and, therefore, less costly relays may be employed.

From a practical standpoint it has been found that the feedback apparatus, either the transformer or the condenser, may be of such small size that it may be mounted on the switch plate and does not require extra mounting space on the circuit plates. The present invention therefore provides an economical means for improving the operation of switching apparatus rendering it more reliable and increasing its field of use.

A feature of foreshortened operation under adverse line conditions. By the use of such a transient current an impulse muti lated by adverse line conditions may be made to satisfactorily operate a magnetic device requiring a comparatively strong current. Again by the use of such an arrangement the switching apparatus may be operated over lines loaded by a larger number of parties and service may thus be provided to a larger number of subscribers.

Another feature of the invention is the employment of a characteristic transient current produced by the rise of current in a circuit including an impedance, making use of the fact that such transient is of high initial and a gradually diminishing value, to fortify and sustain the operation of a relay. Where the said impedance is inductive the transient may be transformed into a surge directed through a secondary winding of a relay. Where in the 5 operation of the Y magnet 20 moves the wipers 17, 18 and 19 on to the first set of terminals of the selected level. In the event of the first trunk being engaged, the sleeve wiper 19 encounters a ground and when the HA relay 14 releases after the initial step of this Y magnet 20, it reoperates from this ground in a circuit from battery, armature 4 and back contact of the HA relay 14, the lower winding thereof, armature 4 and back contact of the XI) relay 13, armature 3 and back contact of the HA relay 14, armature 2 and front contact of the RD relay 12, back contact and armature 1 of the SW relay 10 to the sleeve wiper 19. This reenergizes the Y magnet which in turn steps the Wiper to the next set of terminals in the selected level. If the next trunk is also engaged the sequence of operations just described takes place once more. This interaction between the sleeve lead, the HA relay 14 and the Y magnet 20 recurs until the wipers step to a set of terminals connected to an idle trunk or until all the trunks outgoing from the level are found busy.

When the Wipers are stepped to the terminals of an idle trunk, the absence of ground on the sleeve lead prevents the operation of the HA relay 14,

the armature 4 and back contact of the HA relay 14, the lower winding thereof, armature 4 and back contact of the XD relay 13, armature 3 and back contact of the HA relay 14, winding of the SW relay 10,

12. Moreover, when the SW relay 10 operates, the circuit of the lower winding of the HA relay 14 is shunted from battery, primary of 20, front contact and armature 4 of the SW relay 10, to the Winding thereof.

2 and 3 of the SW relay 10 and it releases, thereby opening the circuit of the RD relay 12 so that in a short period of time, measured by the slow releasing characteristics of this relay, it becomes released. At this stage the to the sleeve lead over the sleeve wiper 19, but the ground the RD relay 12 remains connected until this ground from the succeeding circuit may be transmitted back to hold the SW relay operated during the succeeding conversational period. During this period the SW relay, therefore, remains operated from this ground transmitted back from the succeeding circuit.

In the event of all trunks outgoing from the level being busy the tip, ring and sleeve wipers 17, 18 and 19 respectively are stepped to the eleventh position and the overflow springs are actuated. Spring 5' moves from connection with spring 4 to connection with spring 6 so that busy tone is now transmitted back toward the calling subscriber instead of dial tone transmitted heretofore. A circuit is also established from ground, springs 2 and 3 of the overflow set to the lower winding of the HA relay 14, to hold this relay steadily operated. When the subscriber clears the line after receiving busy tone, the CB relay 9 releases, causing the release of the RD relay 12. Thereupon a circuit is established from ground, armature 5 and back contact of the SW relay 10, springs 5 and 6 of the X off normal set, armature 3 and back through the winding of whereby this magnet and sleeve wipers to At the same time the sleeve lead to prevent and to hold the finder contact of the RD relay 12, the Z release magnet 11 to battery, operates and causes the tip. ring return to their normal positions.

Z magnet places a ground on the any operation of the SW relay 10 7 operated until the wipers of this selective switch have reached their normal position.

Under normal ments of another embodiment of the The C5 relay 21 corresponds exactly to the CB relay 9, the RD relay 22 corresponds to the RD relay 12 and the LP relay 23 corresponds to the HA relay 14.

In the present case, therefore,

when the CB relay 21 first operates, it operates the RD slow release relay 22 of relay is released and the conby the movement of armature 2 of the LP relay from ground to battery.

current, and a second operating winding on said second relay included in the path of said transient current whereby the operation of said second relay by said first winding cessive leakage, a second relay in a local circuit controlled by said first relay, said second relay having an auxiliary winding, a magnetic device responsive to comparatively strong currents operated by said second relay, a transformer having one of its windings connected in series with said magnetic device and having another of to the operating currents of any of said magnets when 10 controlling the operation of each of said circuits.

References Cited in the file of this patent UNITED STATES PATENTS Cummings Aug. 7, 1923 West May 7, 1940 Kovalsky Aug. 26, 1941 Tedder Nov. 9, 1948 Dodd Jan. 13, 1953 y 9, 1955 s. G. MEADOWS ET AL 2,713,656

ELECTRIC MOTOR FOLLOW-UP SYSTEM Filed April 2, 1955 By M A/[Umw 

